The prior art sequencing control circuits have included a number of different stepping relays which were electromagnetic relays capable of achieving a sequence of four different conditions of a motor and load. The load of the motor has included a garage door operator motor and the four conditions establish run up, stop up, run down and stop down of the raising and lowering type of garage door. The prior art electromagnetic relays were able to achieve these four functions and count control a reversing motor as well as controlling a lamp to illuminate the interior of the garage. The prior art had manual switches as inputs to the electromagnetic relays including a manual push button switch and a remotely controlled radio receiver switch. The transmitter controlling the receiver switch was often a hand-sized transmitter which would be located in the vehicle to be garaged. Such prior art garage door operators also had load switches such as up and down limit switches and torque or overload switches.
The prior art electromagnetic relays could also provide for a sequence of operation wherein if the garage door upon descending should strike a child or a pet animal, for example, the door would not merely stop due to overload, rather it also would move back toward an open position. This was a safety reverse feature during door closing. The prior art door operator circuits could also provide a time delay so that the lamp illuminating the garage could remain on for a period of one or two minutes even after the door had closed and the motor had been deenergized. Such prior art sequencing control circuits of the electromagnetic stepping relay type may be of the type illustrated in U.S. Pat. No. 3,719,005 issued Mar. 6, 1973.
The prior art door operator controls also included the type often used on commercial garage doors wherein a person had to maintain his finger on an "up" button or "down" button in order to have the door continue to move in the desired direction. If one ceased depressing the button the door would stop in a partially opened or closed condition. People familiar with this type of commercial garage door operator would often tend to hold their finger on the push button switch of a residential garage door operator for the entire time that the door was moving. In so doing this kept the actuating coil of the stepping relay energized, hence the ratchet mechanism was not released and the stepping relay was then incapable of responding to a load switch input, e.g. limit switch or torque switch. The same type of dangerous operating condition could occur if there was a short circuit in the push button wiring which would give a continuous input signal to the electromagnetic relay. This means that the door operator motor would not shut off when reaching the limit switch. An even more dangerous condition was that if the door were moving downwardly and a child got trapped under the door, the door would not reverse to move upwardly. If the radio transmitter in the automobile were left on the seat and a package placed on top of it this might depress the push button switch so that the transmitter emitted a continuous signal. This could cause the same type of dangerous condition. Also if a person entered the garage and accidentally knocked a rake or other tool to lean against the push button switch causing a continuous signal, this could also cause the same dangerous condition.
The door operator motor and garage door as a load connected thereto have inertia and in a typical garage door it takes about 0.3 to 0.6 of a second for the motor to accelerate the load to a condition of normal running speed in the motor. The torque switch is usually closed when the motor is at rest and the motor must accelerate to about half speed before this torque switch opens. Also the travel limit switches are often closed at the limit condition of the door and the door must move to release the closed condition of such limit switch. Thus there is a period of about 0.3 to 0.6 of a second wherein an input signal is provided by the torque switch or the limit switch. If a person merely depressed the push button switch for a fraction of a second which was less than the time period of 0.3 to 0.6 of a second, then the door operator circuit could obtain an additional input signal from the then closed limit or torque switch. This additional input signal would again actuate the electromagnetic stepping relay to the next condition which would be a door stopped condition. The person would then have to depress the push button three more times to get the door moving in the desired upward direction.
If the power were to be interrupted while the door was moving upwardly, for example, the door naturally would stop. When the power was restored and the push button again depressed, the door would not move in an upwardly direction instead it would move downwardly toward a closed condition. Accordingly, with the prior art electromagnetic relays, it would take two more depressions of the push button to get the door moving in the desired upward direction.